The traditional PWM dimming method driven by the linear constant-current LED comprises the following steps: as shown in FIG. 1, an input PWM signal is converted into a DC reference voltage VREF through an RC filtering circuit, and the output current of the constant current source circuit is changed according to the DC reference voltage VREF so as to realize dimming. However, as shown in FIGS. 2 and 3, according to such manner of dimming, when the duty cycle of the PWM signal is constant, the input power of the linear constant-current LED driving system is changed when the input mains supply voltage is changed, thereby causing voltage flicker and affecting the overall lighting effect.
Accordingly, the prior art has yet to be improved.